At present, with continuous increase in a size of a display, and continuous improvement of frequency of a driving circuit, it has been very difficult for mobility of an existing amorphous silicon thin film transistor to meet demands, but a thin film transistor (TFT) having a channel formed by a metal oxide semiconductor with a high mobility (hereinafter referred to as a metal oxide TFT) has been gradually widely used in the field of display. The metal oxide TFT has advantages such as high mobility, good uniformity, transparency, and simple fabrication process, which helps to implement a display device of a large size and having a driving circuit with high frequency, and thus, becomes a focus of research.
An amorphous indium gallium zinc oxide is a typical transparent metal oxide semiconductor, which has a good light transmission for visible light. When irradiated by light with a wavelength of 420 nm or more, an I-V curve of the amorphous indium gallium zinc oxide TFT is relatively stable; but when irradiated by ultraviolet light with a wavelength less than 420 nm, the I-V curve of the amorphous indium gallium zinc oxide TFT starts to drift by a large margin, and is very unstable. This is because energy of ultraviolet light is already higher than a forbidden bandwidth of the amorphous indium gallium zinc oxide, resulting in drift of the I-V curve of the amorphous indium gallium zinc oxide TFT. Thus, it is a difficult point in the art to ensure light stability of the oxide semiconductor TFT.